* [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> On 14 Feb 2008 at 17:35, Jakub Jelinek wrote:
>
> > Where do you see a mispredicted branch?
>
> try it with -Os (gentoo gcc 4.2.2):
>
> 0000000000000000 <foo>:
> 0: 48 83 ec 58 sub $0x58,%rsp
> 4: 65 48 8b 04 25 28 00 00 00 mov %gs:0x28,%rax
> d: 48 89 44 24 48 mov %rax,0x48(%rsp)
> 12: 31 c0 xor %eax,%eax
> 14: 48 89 e7 mov %rsp,%rdi
> 17: e8 00 00 00 00 callq 1c <foo+0x1c> 18: R_X86_64_PC32
>
> bar+0xfffffffffffffffc
> 1c: 48 8b 54 24 48 mov 0x48(%rsp),%rdx
> 21: 65 48 33 14 25 28 00 00 00 xor %gs:0x28,%rdx
> 2a: b8 06 00 00 00 mov $0x6,%eax
> 2f: 74 05 je 36 <foo+0x36>
> 31: e8 00 00 00 00 callq 36 <foo+0x36> 32: R_X86_64_PC32
>
> __stack_chk_fail+0xfffffffffffffffc
> 36: 48 83 c4 58 add $0x58,%rsp
> 3a: c3 retq
ah, that's what my kernel uses too - and CONFIG_CC_OPTIMIZE_FOR_SIZE=y
is the default for Fedora too.
hm, especially those big addressing mode mov's and xor's look rather
nasty.
Ingo
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